The present invention relates to a mass spectrometer. The preferred embodiment relates to an Electron Transfer Dissociation (“ETD”) reaction or fragmentation device wherein positively charged analyte ions are fragmented upon reacting or interacting with negatively charge reagent ions. The analyte ions and reagent ions are preferably cooled to near thermal temperatures within a spherical ion trapping volume formed within a modified ion tunnel ion trap. As a result, analyte ions are fragmented with a greater efficiency. The resulting fragment or product ions are also preferably cooled to near thermal temperatures and may then be mass analysed by a Time of Flight mass analyser.
It is known to contain ions having opposite polarities simultaneously within an ion trap. It is also known that the effective potential within an ion trap is independent of the polarity of the ions so that, for example, a quadrupole ion trap may be arranged to store simultaneously both positive and negative ions.
Ion-ion reactions such as Electron Transfer Dissociation (“ETD”) and Proton Transfer Reaction (“PTR”) have been studied in a modified commercial 3D ion trap. Electron Transfer Dissociation involves causing highly charged positive analyte ions to interact or collide with negatively charged reagent ions. As a result of an ion-ion reaction the positively charged analyte ions are caused to fragment into a plurality of fragment or product ions. The fragment or product ions which are produced enable the parent analyte biomolecule ion to be sequenced.
Electron Capture Dissociation is also known wherein analyte ions are fragmented upon interacting with electrons. However, a particular advantage of Electron Transfer Dissociation reaction or fragmentation as compared with Electron Capture Dissociation is that it is not necessary to provide a relatively strong magnetic field in order to constrain the path of electrons so as to induce ion-electron collisions.
Electron Transfer Dissociation experiments have been attempted in a 3D or Paul ion trap. A 3D or Paul ion trap comprises a central ring electrode and two end-cap electrodes having a hyperbolic surface. Ions are confined within the 3D or Paul ion trap in a quadrupolar electric field in both the axial and radial dimensions. However, although Electron Transfer Dissociation has been investigated using a 3D or Paul ion trap very little if any actual fragmentation of positively charged analyte ions has been observed within such a 3D ion trap.
It is therefore desired to provide an improved Electron Transfer Dissociation reaction or fragmentation device.